1. Field of the Invention
The present invention relates to a decorative sheet for construction, a decorative concrete product for construction using the decorative sheet, and processes for preparing them. In particular, it relates to a decorative sheet for construction which enables a decorative layer with a backing layer having a natural stone-like pattern or the like to be transferred to an interior or exterior surface of a construction such as a wall, a gatepost, a fence, a passage, a poolside, a pavement, a curb of a road or of a plot in a park, or a surface of other various types of constructions; a decorative concrete product with such a decorative layer with a backing layer transferred thereto by the use of the decorative sheet; and a processes for preparing them.
2. Related Art Statement
To decorate interior and exterior surfaces of constructions and/or to impart improved water resistance thereto, various surface finishes are generally given to inner and outer walls, and floors of constructions and the like.
For example, in application of inner and outer walls and a floor in a construction site, there has heretofore been conducted such a procedure by a skilled artisan that a mixture of a concrete or mortar with an aggregate is prepared in situ and applied, and thereafter, the surface of the resultant is subjected to so-called scrubbed finish by partially scrubbing it off with water or so-called scraped finish by partially scraping it off with a wire brush, or coated with a coating, or tiled. Alternatively, in a case of a construction of large scale, surface-decorated large-sized interior or exterior concrete products such as precast concrete panels or precast concrete blocks are preliminarily manufactured in a factory, and transported into a construction site and constructed there into inner or outer walls and the like.
By the various types of surface finish, aesthetic appearance and solid-looking are imparted to constructions and/or practically desired durability, water resistance and the like are effectively attained. In such various types of finish, in particular scrubbed finish, scraped finish and the like, however, technical skills of skilled artisans are required, and yet it is difficult to attain appearance with just intended pattern and/or color. Further, such finishing operations are likely, from the nature thereof, to be prevented from being carried out in rainy days, i.e., these finishing operations have great problem of susceptibility to weather.
To solve these disadvantages inherent in such finishing operations on constructions, a number of attempts have been proposed.
Japanese Unexamined Utility Model Publication No.64438/1986 discloses a decorative sheet for construction which comprises a resin sheet, an adhesive layer formed on one side of the resin sheet, and aggregates such as sand, gravel or the like deposited over the adhesive layer. According to the reference, concrete is applied onto a construction body, and while the concrete is yet unhardened, the decorative sheet for construction is uniformly pressed against the concrete in such a manner that the side of the decorative sheet on which aggregates such as sand or gravel are deposited is in contact with the concrete, and after completion of hardening of the concrete, the resin sheet is peeled off to thereby transfer the decorative layer comprising an adhesive and aggregates such as sand or gravel onto the surface of the construction.
However, when such a decorative sheet for construction is used, since the aggregates are likely to be insufficiently bonded to each other via the adhesive, detachment of the aggregates tends to occur after the removal of the resin sheet. Accordingly, durability is liable to be poor. In the reference, there is also disclosed an embodiment aiming at improving durability, in which after the deposition of the aggregates such as sand or gravel over the adhesive, a coating film is formed thereon by spraying a resin, glue or the like to strengthen the bonding between the aggregates. It is, however, confirmed that because of poor penetration of the resin or glue into fine voids between the aggregates, such a coating film formed only therefrom cannot sufficiently strengthen the bonding between the aggregates. Further, adhesion between the concrete and the resin or glue is likely to be poor, and hence there occurs a phenomenon that the decorative layer transferred is peeled from the concrete at the time of the removal of the resin sheet. In addition, when a paper sheet is used instead of the resin sheet, the paper sheet is liable to be broken during its removal to partially remain unreleased. Accordingly, smooth release of the paper sheet is hardly expected.
Japanese Unexamined Patent Publication No.277408/1986 discloses a method which comprises forming an adhesive layer on one side of a paper sheet, depositing aggregates such as sand or gravel on the adhesive layer, pressing the resulting sheet against concrete applied as a body of a construction while the concrete is still unhardened in such a manner that the surface on which the aggregates such as sand or gravel are deposited is in contact with the concrete, and removing the paper sheet after completion of hardening of the concrete to fixedly transfer the aggregates such as sand or gravel to the surface of the concrete. Also in this method, the aggregates are incompletely bonded by the adhesive and accordingly liable to detach, thereby leading to poor durability. Further, as specific methods for removing the paper sheet, washing off with water, burning off, abrasion and the like are mentioned. For example, however, water running from upper potion to the lower portion in the method of washing off with water, and use of fire device in the method of burning off make cumbersome limitations in construction, thereby inevitably leading to poor constructional efficiency and increased cost.
To solve the above-mentioned problems, the present inventors have made intensive and extensive studies, and as a result, they have developed a decorative sheet for construction which comprises a resin film, preferably a polypropylene film; a layer formed thereon as a decorative face layer including inorganic aggregates and an additive; and a backing layer formed on the decorative face layer, and they have already filed a patent application relating thereto (Japanese Unexamined Patent Publication No.299833/1990). In this decorative sheet for construction, the backing layer is formed on the resin layer as a decorative face layer including inorganic aggregates to cause to penetrate into fine voids between the inorganic aggregates, thereby further strengthening the bonding between the aggregates.
However, it has disadvantageously often occurred that during transportation of the decorative sheet for construction to a construction site to carry out the application, the polypropylene film and a portion of the decorative face layer unexpectedly separate from each other. Further, it has been found that since an unexpanded one is used as the polypropylene film, the surface thereof is likely to be damaged when a member having an acute tip abuts upon the surface. It has further been found that in the case where a polystyrene film is used instead of the polypropylene film, although separation during transportation does not occur, if removal of the surface polystyrene film is conducted without close attention after application at a predetermined position and transfer of the decorative face layer to a placed concrete, the film is broken and hardly removed in part.
Further, it has been confirmed that in producing a decorative concrete product such as a decorative concrete panel, if the surface film is made of a polypropylene or polystyrene, the surface film may undergo deformation due to contraction by generated heat, thereby disadvantageously causing a partially incomplete transfer of the decorative face layer.